Data communication apparatus

ABSTRACT

A data communication apparatus includes a communication section that performs a pre-communication protocol and transmits data to a destination terminal. A memory stores data and communication parameters corresponding to each destination terminal, the communication parameters being utilized to perform communication with the destination terminal. When data corresponding to a destination terminal data is stored in the memory, a controller performs the pre-communication protocol with the destination terminal, using the stored communication parameters corresponding to the destination terminal. When a communication error occurs in a communication with a particular destination terminal having data stored in the memory, a memory controller deletes communication parameters corresponding to the particular destination terminal from the memory.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 09/077,290 now U.S.Pat. No. 6,426,946, filed on May 28, 1998, which is the National Phaseof International Application No. PCT/JP97/03905, filed Oct. 28, 1997,the contents of which are expressly incorporated by reference herein intheir entireties. The International Application was not published underPCT Article 21(2) in English.

The present invention relates to a data communication apparatus whichshortens the time needed for a pre-communication protocol that iscarried out prior to actual communication in data communication using amodem, such as facsimile communication.

BACKGROUND ART

Recently, this type of data communication apparatus performs datacommunication using a V.34 modem (28.8 kbps) which is specified by theITU-T. The ITU-T also recommends T30 ANEXF (so-called Super G3) asfacsimile communication standards using the V.34 modem for facsimilemachines. A pre-communication protocol for facsimile communication iscarried out according to the standards, after which communication ofimage data is executed.

Such a communication protocol will be explained based on the sequencechart illustrated in FIG. 13. FIG. 13 is a control signal chart for apre-protocol for facsimile communication according to prior art.

Referring to FIG. 13, reference character 13 a denotes a communicationprotocol for selecting a modulation mode from among a V34 half duplex,V34 full duplex, V17 half duplex, etc. Reference character 13 b denotesa communication protocol for implementing line probing to check a lineand determine various kinds of parameters. Reference character 13 cdenotes a communication protocol for modem training. Reference character13 d denotes a communication protocol for setting a modem parameter.Reference character 13 e denotes a communication protocol for exchanginga facsimile control signal. Reference character 13 f denotes a datacommunication protocol for the primary channel. The upper side in thediagram is a sequence for a caller modem, and the lower side is asequence on an answer modem, and the sequences progress from left toright.

The above communication protocols will be discussed specifically.

First, in the communication protocol 13 a for selecting a modulationmode and communication protocol, which permit communication between acaller modem and an answer modem, are selected through a V.21 modem (300bps, full duplex) after a line connection is established. A facsimilemachine using a V.34 modem selects a V.34 modem as the modulation modeand facsimile communication as a communication protocol.

Then, the communication protocol 13 b for line probing checks the lineby transmitting a line probing tone from the caller modem and receivingit on the answer modem, and selects a training parameter based on theresult of the line inspection.

In the communication protocol 13 c for modem training, the caller modemsends training signals based on the training parameter selected underthe line probing communication protocol 13 b, while the answer modemreceives the training signals, learns a filter coefficient for anadaptive equalizer for compensating the line characteristic and checksthe reception quality of the training signals.

In the communication protocol 13 d for selecting a modem parameter,modem parameters are negotiated between the caller modem and answermodem in full duplex communication at 1200 bps, and an optimal modemparameter is selected from the modem parameters preset in the apparatus,the result of the line inspection and the inspection of the receptionquality of the training signals.

The communication protocol 13 e for a facsimile control signal is anordinary facsimile protocol to execute negotiation of facsimile controlsignals NSF, CSI, DIS, TSI, DCS, CFR, etc. in full duplex communicationat 1200 bps.

In the data communication protocol 13 f, the caller modem sends imagedata and the answer modem receives the image data, in half duplexcommunication at 2400 bps to 28.8 kbps. In the case of performingcommunication at the maximum communication rate of 28.8 kbps, image datacan be communicated in approximately three seconds per a sheet of paperof size A4.

The aforementioned modem performs communication in accordance with thetraining parameter selected under the communication protocol 13 b forcommunication line probing and the modem parameter selected under thecommunication protocol 13 d for selection of a modem parameter. Tocompensate the line characteristic, the receiver modem executescommunication using the filter coefficient that has learned in the modemtraining 13 b. This ensure optimal data communication according to theline quality.

The above-described prior art structure involves five channels of apre-protocol before starting sending image data after lineestablishment, and thus requires about 7 seconds. By contrast, sinceelectric transmission of a single sheet of image data at the maximumcommunication rate of 28.8 kbps takes about 3 seconds, the pre-protocolrequires over 60% of the entire time of 11 seconds required fortransmission of one sheet of an original including the post-protocol ofabout 1 second. This time needed for the pre-protocol gets greater asthe number of transmission/reception lines increases, and generateswasteful time and communication cost.

DISCLOSURE OF INVENTION

Accordingly, it is an object of the present invention to provide a datacommunication apparatus capable of shortening the time forpre-communication protocol including setting of various parameters for amodem and the modem training time.

A data communication apparatus according to this invention comprisescommunication means for executing pre-communication protocol forexchanging a communication function with a communication destination andtransmission and reception of data; storage means for storing aplurality of communication parameters in association with identificationnumbers of apparatuses to be the communication destination; and controlmeans for, when an apparatus of the communication destination is acommunication apparatus registered in the storage means, activating thecommunication means using the communication parameter associated withthat communication destination, read from the storage means, to therebyexecute data communication according to a short protocol, and, when anapparatus of the communication destination is not a communicationapparatus registered in the storage means, activating the communicationmeans using a communication parameter acquired under a communicationprotocol for that communication to thereby execute data communication.

More specifically, at the time of carrying out a normal communicationprotocol, a modulation mode, a communication protocol, a modem parameterand a modem's optimal training time, etc., which are set by fourcommunication channels, e.g., a communication channel for selecting amodulation mode, a communication channel for implementing line probing,a communication channel for modem training, and a communication channelfor setting a modem parameter, are stored for each destinationcommunication apparatus, and subsequent communication is implementedbased on the stored information.

At this time, the control means determines if an apparatus of thecommunication destination is a communication apparatus registered in thestorage means based on either whether or not an operation key forspecifying a memory address in the storage means where an identificationnumber and a communication parameter of the communication destinationare stored has been depressed, or sender identification informationinformed from an exchange.

At this time, the control means transmits an instruction signal of thesame modulation system as a call-initiating menu signal in place of thecall-initiating menu signal to thereby inform the communicationdestination of execution of a short protocol.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a reference structural diagram of a facsimile machine to whicha data communication apparatus according to a first embodiment of thisinvention is adapted;

FIG. 2 is a functional structural diagram of a digital signal processor(DSP) according to this embodiment;

FIG. 3 is an explanatory diagram showing tones of a line probing tonesignal according to this embodiment;

FIG. 4 is a block diagram of a training reception section according tothis embodiment;

FIG. 5 is an explanatory diagram illustrating calculation of an optimaltraining time according to this embodiment;

FIG. 6 is a flowchart illustrating a control operation at the time oftransmitting an outgoing signal according to this embodiment;

FIG. 7 is a memory structural diagram of a short protocol registrationmemory according to this embodiment;

FIG. 8 is a flowchart illustrating a control operation at the time ofreceiving an incoming signal according to this embodiment;

FIG. 9 is a control signal chart for a normal protocol at the time ofregistering a short protocol according to this embodiment;

FIG. 10 is a control signal chart at the time of executing the shortprotocol according to this embodiment;

FIG. 11 is a flowchart illustrating a control operation when a telephonenumber informing service of a data communication apparatus according toa second embodiment of this invention;

FIG. 12 is a control signal chart when the telephone number informingservice according to this embodiment is used; and

FIG. 13 is a control signal chart showing a normal protocol for aconventional modem.

BEST MODES FOR CARRYING OUT THE INVENTION

A data communication apparatus according to a first embodiment of thepresent invention will now be described in detail with reference to theaccompanying drawings. FIG. 1 is a basic block diagram of a facsimilemachine to which this invention is adapted.

Referring to FIG. 1, a scanning module 101 reads the image of anoriginal, and a printing module 102 records and outputs a receivedimage. A controller 103 performs the general control of the apparatus,and also carries out control to encode and decode image signals andexecute a communication protocol.

A modem 104, which implements every modulation and demodulation in afacsimile communication protocol that is specified in T.30 ANEXF of theITU-T, comprises a digital signal processor (DSP) 104 a for performingmodem's signal processing and an analog front end module (AFE) 104 bhaving both A/D conversion and D/A conversion functions.

A network control unit (NCU) 105 controls dialing and calling to a line106. An operation module 107 comprises various kinds of key inputswitches, such as dial keys and a start key, and a display unit fordisplaying information. Various sorts of operations of the apparatus areperformed through this operation module 107.

A memory 108 stores various sorts of information for execution of ashort protocol in the case of communicating with a communicationdestination which has a short protocol function. In this embodiment,information like a telephone number and a modem parameter is stored asshown in FIG. 7 which will be discussed later.

A modem parameters is set by setting a power reduction value indicativeof signal power and a time value indicative of a training time, andperforming various selections, such as carrier frequency selection forselectively setting either a high level or a low level, preemphasisfilter selection, symbol rate selection for selectively setting fivelevels of rates that are transmitted for an eye pattern and selection ofa training constellation point.

The functional structure of the digital signal processor 104 a of themodem 104 will now be discussed with reference to FIG. 2.

A modem controller 201 controls interface with the controller 103 andvarious modem functions. This modem controller 201 has a plurality offunctional modules which will be discussed below and which are executedby ordinary software.

A tonal transmission module 202 sends various tonal signals inaccordance with communication protocols. A tonal detector 203 identifiesa tonal signal sent from a communication destination. A V.21 modem 204is a modem which conforms to Recommendation V.21 of the ITU-T (300 bps,full duplex). An INFO modem 205 is a modem which conforms toRecommendation V.34 of the ITU-T (600 bps, full duplex), and is used ina start procedure in the communication protocol for line probing and ashort protocol.

A control channel modem module 206 is a control channel modem (1200 bps,full duplex) specified by Recommendation V.34 of the ITU-T, and is usedin setting a modem parameter for a primary channel modem and in acommunication protocol for a facsimile control signal.

A primary channel modem module 207 is a primary channel modem (2400 bpsto 28.8 kbps, half duplex) specified by Recommendation V.34 of theITU-T, and is used in communicating image data.

A line probing transmission module 208 sends line probing tones whichare specified by Recommendation V.34. The line probing tone are combinedsignals of 21 kinds of tonal signals of 150 Hz to 3750 Hz as shown inFIG. 3.

A line probing reception module 209 receives the line probing tones froma communication destination to inspect the line. Specifically, the lineprobing reception module 209 performs spectrum analysis on the receivedsignals using the fast Fourier transform algorithm to select the optimalsymbol rate and carrier frequency for the primary channel modem 207 andselect other modem parameters.

A training transmission module 210 sends training signals for the V.34modem, and a training reception module 211 receives the training signalsfrom a communication destination and learns a filter coefficient of anadaptive equalizer to compensate line distortion.

Next, this training reception module 211 will be discussed withreference to the block diagram of FIG. 4.

A demodulator 401 converts a received training signal Sp, which hasundergone A/D conversion in the analog front end module 104 b, to acomplex baseband signal Yb from the passband. An adaptive equalizer 402compensates line distortion with respect to the baseband signal Yb andoutputs a received signal Yr. A decision circuit 403 determines adecision point Yd for determining the amount of shift of a point on aneye pattern, and outputs the decision point Yd. A subtracter 404subtracts the decision point Yd from the received signal Yr and outputsan error signal Er. Note that Yb, Yr, Yd and Er are complex signals. Theerror signal Er is supplied to the adaptive equalizer 402, which learnssuch an internal filter coefficient as to reduce this error signal Er.The learned internal filter coefficient is used as a reception filtercoefficient in the primary channel modem module 207.

An absolute value unit 405 computes the absolute of the error signal Er.An LPF 406 is a low-pass filter for smoothing the output signal, Ea, ofthe absolute value unit 405. The output signal of the LPF 406 is an EQMsignal which represents the degree of compensation for the linedistortion of the adaptive equalizer 402, and the smaller this EQMsignal is, the more sufficiently the line distortion is compensated.

An equalization analyzing module 407 analyzes the ability of theadaptive equalizer 402 to compensate the line distortion, from the EQMsignal. As shown in FIG. 5, the equalization analyzing module 407observes the amount of change in the EQM signal from the beginning oftraining, and computes the time at which the absolute value of theamount of change becomes smaller than a given value, as the optimaltraining time. The equalization analyzing module 407 also computes theratio (SN) of the training signal power (the absolute value of a pointfrom the origin in an eye pattern) to noise power (an error in the pointin the eye pattern) which is the final value of the EQM signal. Theoptimal training time is used as the training time in executing a shortprotocol, and the SN ratio is used in selecting the data transfer rateof the primary channel modem 207. When a short protocol is to be carriedout, the optimal training time is not computed.

The operation of the thus constituted data communication apparatus willbe discussed below.

To begin with, the operation of a caller modem will be discussed. FIG. 6is a flowchart illustrating a control operation of a facsimile machineaccording to this embodiment at the time of transmitting an outgoingsignal.

In step (hereinafter referred to as “ST”) 601, calling is initiated inaccordance with the telephone number of a transmission destination and atransmission start instruction from the operation module 107, the memory108 is searched to check if the telephone number of the transmissiondestination is registered for a short protocol. When registration is notmade, the flow proceeds to ST 602 to make dialing.

In ST 603, facsimile communication is carried out in a normalcommunication protocol based on T.30 ANEXF of the ITU-T.

In ST 604, it is checked if the destination machine supports a shortprotocol communication. This check is accomplished by detecting a flagindicating that a short protocol communication is possible, in a fieldfor the non-standard protocol signal NSF in a facsimile control signal.

In ST 605, when the destination facsim having a short protocol functioncan be confirmed, the transmitter mode executes a normal protocol andregisters various parameters necessary to implement a short protocol.The contents to be registered for a short protocol are, for example,selected information on the power reduction value and carrier frequency,the optimal training time, selected information on a non-lineardistortion compensation value, etc. Those information are stored in thememory 108 in accordance with the memory structure of the short protocolregistration memory illustrated in FIG. 7.

When a flag indicating that a short protocol communication is possiblecould not be detected in ST 604, communication is implemented in anormal communication protocol the in ST 606.

In the case of the short protocol registration in ST 601, dialing ismade and a short protocol communication is carried out in ST 607 and ST608. In the short protocol communication, a modem parameter in the shortprotocol registration memory 108 is sent to the transmission destinationin the start procedure to execute the transmission operation accordingto the modem parameter. This eliminates the need for negotiation withthe receiver, thus shortening the communication time.

In ST 609, it is determined if there is a communication error, and inthe case of no communication error, the flow proceeds to ST 610. In ST610, the rate of data errors in communication is determined, and whenthere are not many data errors, the process will be terminated. Thiserror rate decision has only to be made based on, for example, thenumber of resends in ECM.

When it is determined in ST 609 that there is a communication error andwhen it is determined in ST 610 that there are multiple data errors, thecontents of the short protocol registered for the transmissiondestination are erased from the memory 108 in ST 611, after which theprocess will be terminated.

The reason why a communication control protocol is executed inaccordance with various communication parameters, which have beenprestored in association with destination telephone numbers in the abovemanner, is based on the following.

Generally, facsimile machines are often connected one to a single line.As communication is often carried out in the same mode with respect tothe same communication destination, therefore, a control protocol forexchanging the data communication mode need not be executed every timecommunication is carried out if the previous communication mode isstored in a transmitting apparatus and a receiving apparatus.

Because the quality of a telephone line has been improved due to therecent widespreading of digital exchanges, therefore, there becomes nodifference in line characteristics which originates from a difference inconnection paths. As a result, similar line characteristic andcommunication quality are always provided for the same communicationdestination. If previous modem parameters are stored, therefore, it isunnecessary to conduct a communication protocol associated with lineprobing for each communication.

Further, the training time, which is set in accordance with the learningtime for the filter coefficient of the adaptive equalizer of a receivingapparatus, is generally set to the length that can be adapted for everyline. When communication is implemented over a line with a highcommunication quality, therefore, the learning time for the filtercoefficient can be shorter than the normally set one, so that thetraining time may be wasted. In view of the above, the execution time ofa pre-communication protocol is shortened by carrying out thepre-communication protocol using a prestored communication parameter.

Next, the operation of the receiver of an answer modem will beexplained. FIG. 8 presents a flowchart illustrating a control operationfor a pre-communication protocol at the time a facsimile machineaccording to this embodiment receives an incoming signal.

In ST 801, after receiving a reception command sent over the line 106, amodified answer tone ANSam is sent.

In ST 802, it is detected whether to receive a quick tonal signal (QTS)indicating a short protocol or a call menu signal CM from the callermodem, while sending the ANSam.

In ST 803 and ST 804, communication is executed using a registeredcommunication parameter when the QTS signal is detected, whilecommunication is executed in a normal protocol according to the T.30ANEXF of the ITU-T when the CM signal is detected. When the receiver isequipped with a function to conduct a short protocol, a short protocolregistration flag indicating that the local apparatus has the shortprotocol capability and the optimal training time are described in theNSF field of the facsimile control signal at the time of implementingcommunication in the normal protocol. The transmitter registers a shortprotocol for this receiver based on the information in the NSF field.

The normal communication protocol according to Recommendation V.34 willnow be discussed. Registering various parameters for use in executing ashort protocol is conducted in accordance with the information in theNSF field in this normal communication protocol.

FIG. 9 is a control signal chart for this communication protocol. Aftera line connection is established, a communication protocol 9 a forselecting a modulation mode is performed, followed by a communicationprotocol 9 b for line probing, a communication protocol 9 c for modemtraining, a communication protocol 9 d for setting a modem parameter, acommunication protocol 9 e for a facsimile control signal, and then adata communication protocol 9 f for sending image data.

The communication protocol 9 a for selecting a modulation mode willspecifically be discussed below. A caller modem sends a caller numberidentification signal CNG, and an answer modem sends a modified answertone ANSam. Thereafter, the caller modem sends a call menu signal CMindicative of the functions of the caller modem, such as the modulationmode and communication protocol, while the answer modem sends a jointmenu signal JM indicative of a common communication capability inaccordance with the contents of the received signal CM. Whenacknowledging this joint menu signal JM, the caller modem sends a CMterminal signal CJ and then proceeds to the communication protocol 9 bfor line probing. The answer modem detects the CM terminal signal CJwhile sending a joint menu signal JM, and then also goes for thecommunication protocol 9 b for line probing. The signals CM, JM and CJare communicated through the V.21 modem 204 (300 bps, full duplex).Based on the exchange of those signals, a facsimile machine with a V.34modem, for example, can select a modulation mode for the V.34 modem anda facsimile communication protocol as the communication protocol.

Next, the communication protocol 9 b for line probing will be described.The caller modem sends INFO0c indicative of a communication capability,such as the preset modulation rate and carrier frequency for the V.34modem, and line probing tones L1 and L2. The answer modem sends INFO0aindicative of the mentioned, preset communication capability, andreceives the line probing tones. The line probing tones are combinedsignals of 21 kinds of tonal signals of 150 Hz to 3750 Hz as shown inFIG. 3.

The answer modem receives the line probing tones, performs spectrumanalysis on the received signals using the fast Fourier transformalgorithm to select the optimal symbol rate and carrier frequency forthe primary channel modem 207 and select other modem parameters. Theanswer modem selects a communicatable training parameter from theselected contents and the contents of INFO0c and INFO0a, sets INFO0h andsends the training parameter and INFO0h.

The aforementioned INFO0c, INFO0a and INFO0h are communicated throughthe INFO modem 205 (600 bps, full duplex) shown in FIG. 2. Thiscommunication protocol uses tones B and iB (having a phase of 180degrees to the tone B) of the caller modem, and tones A and iA (having aphase of 180 degrees to the tone A) of the answer modem, as responsesignals for accomplishing synchronization.

Next, the communication protocol 9 c for modem training will bedescribed. The caller modem sends training signals S, iS, PP and TRNusing the training parameter of the aforementioned INFO0h sequence. Theanswer modem receives the training signals and learns the filtercoefficient of the adaptive equalizer 402 for compensating the linecharacteristic, or computes the optimal training time and noise powerratio SN in the equalization analyzing module 407.

The communication protocol 9 d for setting a modem parameter will now bediscussed. The caller modem and the answer modem send protocol syncsignals PPh and ALT, a modem parameter MPh associated with datacommunication and an acknowledge signal E for the MPh from the oppositeside, so that the caller modem and the answer modem exchange the MPh.The MPh of the caller modem is a modem parameter preset in the callermodem, while the MPh of the answer modem is a modem parameter, which hasbeen selected from a preset modem parameter, the result of inspectingthe received line probing tones and the SN computed from the receivedtraining signals. The communication protocol for setting a modemparameter is carried out using the control channel modem module 206(1200 bps, full duplex) shown in FIG. 2.

Next, the communication protocol 9 e for a facsimile control signal willbe described. First, the answer modem sends a non-standard protocolsignal NSF, a called station identification signal CSI, and a digitalidentification signal DIS. The answer modem sets, in the NSF field, aflag indicating that it has a short protocol capability and the optimaltraining time calculated in the equalization analyzing module 407,before transmission.

After sending the NSF, CSI and DIS and acknowledging that the answermodem has a short protocol capability, the communication apparatus ofthe caller modem sends a transmitting station identification signal TSIand a digital command signal DSC. At that time, the communicationapparatus of the caller modem sets a short protocol registration flagand stores various communication parameters, exchanged in the currentcommunication protocol, in the memory 108 in association with thedestination's telephone number. After receiving the TSI and DCS, theanswer modem sends a reception preparation acknowledgement CFR.

When one of the caller modem and answer modem does not have a shortprotocol capability in other cases than the above-discussed ones, thecaller modem does not set the short protocol registration flag. In thiscase, therefore, a communication protocol for a facsimile control signalis executed using the control channel modem module 206 (1200 bps, fullduplex) in accordance with the ordinary V.34 protocol.

Finally, the data communication protocol 9 f for the primary channelwill now be discussed. Communication here is implemented by using amodem parameter, which is determined in accordance with the trainingparameter of the INFO0h sequence and the MPh and satisfies both thecaller modem and the answer modem.

The caller modem sends protocol sync signals S, iS, PP and B1 for theprimary channel, and then sends PIX (image data). The answer modemreceives the protocol sync signals S, iS, PP and B1 followed by the PIX(image data).

Communication here is carried out with the primary channel modem module207 (1200 bps to 28.8 kbps, half duplex), and particularly, reception bythe primary channel modem module 207 of the answer modem is so designedas to compensate line distortion using the filter coefficient that hasbeen learned by the adaptive equalizer 402. At the maximum communicationrate of 28.8 kbps over the primary channel, communication can be done inabout 3 seconds per a single sheet of size A4.

As apparent from the above, the communication protocol in the case of aregistered short protocol is carried out in the normal protocol asrecommended by the T.30 ANEXF of the ITU-T. As a short protocol isregistered in the memory 108 of the caller modem, communication can beimplemented using the registered short protocol from the next time.

A communication protocol in the case of carrying out a short protocolwill now be discussed specifically.

FIG. 10 is a control signal chart for a communication protocol at thetime of executing a short protocol, and illustrates a communicationprocess from the establishment of a line connection up to communicationof image data. After a line connection is established, a communicationprotocol 10 a for initiating a short protocol is performed, after whicha communication protocol 10 c for modem training, a communicationprotocol 10 d for setting a modem parameter, a communication protocol 10e for a facsimile control signal and a data communication protocol 10 ffor sending data (image data) will be carried out in the normalcommunication protocol.

The communication protocol 10 a for initiating a short protocol will beexplained first. A caller modem sends a caller number identificationsignal CNG, and an answer modem sends a modified answer tone ANSam.After detecting this modified answer tone ANSam, the caller modem sendsa quick tonal signal QTS, and sends tones B and QINFO upon detection ofa response signal tone A from the answer modem. After detecting thequick tonal signal QTS from the caller modem, the answer modem sends thetone A and receives the QINFO from the caller modem.

This quick tonal signal QTS becomes a signal to command transition tothe short protocol. The quick tonal signal QTS is a repeated pattern of“001100110011 . . . ”. Such a tonal signal pattern is used to permit thereceiver to clearly distinguish the received the quick tonal signal QTSfrom a signal pattern of the flag sequence (“011110”) and the tonalsignal pattern of the call menu signal CM (2-bit start bits “10,” 8-bitdata and stop bit of “1”), which are defined by Recommendation T.30 ofthe ITU-T. Moreover, as the quick tonal signal QTS has the samemodulation system as the call menu signal CM, the receiver modem caneasily discriminate whether the communication is to be implemented in ashort protocol or a normal protocol, depending on whether the incomingtonal signal is the quick tonal signal QTS or the call menu signal CM.

In the QINFO sequence, communication is carried out with the INFO modem205 (600 bps, full duplex) in accordance with the contents registered inthe short protocol registration memory for each destination's telephonenumber, i.e., in accordance with the training parameter (INFO0h), theoptimal training time and the selected contents for non-lineardistortion compensation in the case of a registered short protocol, ashas been explained above with reference to FIG. 6.

In the next communication protocol 10 c for modem training, training thetransmitting apparatus and the receiving apparatus is performed inaccordance with the training parameter (INFO0h) of the QINFO sequenceand the optimal training time.

In the communication protocol 10 d for setting a modem parameter, theMPH for the answer modem is set based on the QINFO-based selection ofnon-linear distortion compensation and information on the SN ratiocomputed in the communication protocol 10 c for modem training.

The communication protocol in the short protocol is carried out in sucha manner that the communication protocol for starting the short protocolis executed in an exclusive protocol and the communication protocol formodem training and the subsequent communication protocols are performedin accordance with the recommendation for T.30 ANEXF of the ITU-T,thereby shortening the pre-protocol.

A data communication apparatus according to a second embodiment of theinvention will be described with reference to a flowchart illustrated inFIG. 11.

While registration of a short protocol is conducted in association witha destination's telephone number at the time of dialing on a callermodem in the first embodiment, the second embodiment uses a callertelephone number informing service by an exchange, which has recentlystarted, to register a modem parameter on an answer modem in associationwith the caller telephone number.

Referring to FIG. 11, when a receiver modem is informed of a telephonenumber through the caller telephone number informing service (ST 1101),the receiver modem searches telephone numbers (ST 1102), and executesshort protocol communication (ST 1105) when there is a correspondingtelephone number (ST 1103, ST 1104). When there is no correspondingtelephone number, normal protocol communication is carried out (ST1106).

The above communication control procedures will now be explained withreference to a control signal chart shown in FIG. 12.

When informed of a caller telephone number, a receiver apparatusexecutes a communication protocol 12 a in which the receiving apparatussends a QTS signal to the sender to inform that short protocolcommunication is to be conducted. The subsequent procedures are the sameas described above. That is, a communication protocol 12 c for modemtraining, a communication protocol 12 d for setting a modem parameter, acommunication protocol 12 e for a facsimile control signal and a datacommunication protocol 12 f are executed in order.

Although the QTS signal is different from the QINFO for informing amodem parameter or the like in the above-described embodiment, it iseasy to make a modification of shortening the protocol time by includinginformation of the modem parameter or the like in the QTS signal.

In the embodiment, either the transmitting apparatus or the receivingapparatus registers information such as the modem parameter, the optimaltraining time and the modulation mode in the memory. But, thetransmitting apparatus and the receiving apparatus may both registerthose information in the memories. This allows the transmittingapparatus and the receiving apparatus to skip the communication protocol12 a and start from the communication protocol 12 b upon reception of anincoming signal. In this case, the time for the pre-communicationprotocol is further shortened because such information need not beexchanged in the communication protocol.

According to this invention, as discussed above, normal protocols formodulation mode selection, line probing and modem training are performedand a modem parameter selected then and the optimal training timecomputed then are stored in association with a destination's telephonenumber, so that in the subsequent communication, the communicationprotocol for modulation mode selection and the communication protocolfor line probing can be skipped and the communication protocol for modemtraining can be performed at the optimal training time in accordancewith the stored modem parameter and optimal training time. It istherefore possible to significantly shorten the time for thepre-communication protocol without impairing the communicationcapabilities.

INDUSTRIAL APPLICABILITY

A data communication apparatus in the present invention is appropriatefor the case where a facsimile apparatus according to T30 ANEX(so-called Super G3), which is recommended as a communication standardfor facsimile apparatus-with the V.34 modem recommended by ITU-T, iscommunicating mutually.

1. A data communication apparatus comprising: a communication sectionthat performs a pre-communication protocol with a destination terminal,and transmits data to the destination terminal after thepre-communication protocol; a memory that stores data corresponding toat least one destination terminal, and communication parameterscorresponding to each destination terminal, the communication parametersbeing utilized to perform a communication with the destination terminal;and a controller that, when data corresponding to a destination terminalis stored in said memory, performs the pre-communication protocol withthe destination terminal, using the stored communication parameterscorresponding to the destination terminal, the controller, when acommunication error occurs in a communication with a particulardestination terminal having data stored in said memory, deletescommunication parameters corresponding to the particular destinationterminal from said memory.
 2. The communication apparatus according toclaim 1, the communication parameters comprising at least one of powerreduction value, carrier frequency, optimal training time, andnon-linear distortion compensation value.
 3. The communication apparatusaccording to claim 1, wherein when data corresponding to a destinationterminal is not stored in said memory, said controller performs thepre-communication protocol with the destination terminal, usingcommunication parameters acquired from the destination terminal underthe pre-communication protocol.
 4. The data communication apparatusaccording to claim 1, wherein said controller determines whether or notdata corresponding to the destination terminal is stored in said memorybased on operation of a key that indicates a memory address of saidmemory where the data corresponding to the destination terminal andcommunication parameters are stored.
 5. The data communication apparatusaccording to claim 1, wherein when communication is established for afirst time with a destination terminal having data that is not stored insaid memory, and when the destination terminal can perform a shortprotocol, said controller obtains communication parameters from thedestination terminal under a normal protocol and stores thecommunication parameters in said memory.
 6. A data communicationapparatus comprising; a communication section that performs apre-communication protocol with a destination terminal, and transmitsdata to the destination terminal after the pre-communication protocol; amemory that stores data corresponding to at least one destinationterminal, and communication parameters corresponding to each destinationterminal, the communication parameters being utilized to perform acommunication with the destination terminal; and a controller that, whendata corresponding to a destination terminal is stored in said memory,performs the pre-communication protocol with the destination terminal,using the stored communication parameters corresponding to thedestination terminal, the controller, when a communication error occursin a communication with a particular destination terminal having datastored in said memory, updates the stored communication parameters ofthe particular destination terminal with communication parameters newlyacquired from the particular destination terminal under a normalprotocol.
 7. A data communication apparatus comprising: a communicationsection that includes a modem, that performs a pre-communicationprotocol with a destination terminal, and that transmits data to thedestination terminal after the pre-communication protocol; a memory thatstores data corresponding to at least one destination terminal, andmodem parameters corresponding to each destination terminal, the modemparameters being utilized to perform a communication with thedestination terminal; and a controller that, when data corresponding toa destination terminal is stored in said memory, performs thepre-communication protocol with the destination terminal, using thestored modem parameters corresponding to the destination terminal, thecontroller, when a communication error occurs in a communication with aparticular destination terminal having data corresponding to thedestination terminal stored in said memory, deletes modem parameterscorresponding to the particular destination terminal from said memory.8. A data communication apparatus comprising: a communication sectionthat includes a modem, that performs a pre-communication protocol with adestination terminal, and that transmits data to the destinationterminal after the pre-communication protocol; a memory that stores datacorresponding to at least one destination terminal, and modem parameterscorresponding to each destination terminal, the modem parameters beingutilized to perform a communication with the destination terminal; and acontroller that, when data corresponding to a destination terminal isstored in said memory, performs the pre-communication protocol with thedestination terminal, using the stored modem parameters corresponding tothe destination terminal, the controller, when a communication erroroccurs in a communication with a particular destination terminal havingdata stored in said memory, updates the stored modem parameters of theparticular destination terminal with modem parameters newly acquiredfrom the particular destination terminal under a normal protocol.
 9. Amethod for communicating with a data communication apparatus having amemory storing data corresponding to at least one destination terminaland communication parameters corresponding to each destination terminal,the communication parameters being utilized to perform a communicationwith the destination terminal, the method comprising: performing apre-communication protocol with a destination terminal; performing, whendata corresponding to a destination terminal is stored in the memory,the pre-communication protocol with the destination terminal, using thestored communication parameters corresponding to the destinationterminal; and deleting, when a communication error occurs in acommunication with a particular destination terminal having data storedin the memory, communication parameters corresponding to the particulardestination terminal from the memory.
 10. A method for communicatingwith a data communication apparatus having a memory storing datacorresponding to at least one destination terminal and communicationparameters corresponding to each destination terminal, the communicationparameters being utilized to perform a communication with thedestination terminal, the method comprising: performing apre-communication protocol with a destination terminal; performing, whendata corresponding to a destination terminal is stored in the memory,the pre-communication protocol with the destination terminal, using thestored communication parameters corresponding to the destinationterminal; and updating, when a communication error occurs in acommunication with a particular destination terminal having data storedin the memory, the communication parameters of the destination terminalstored in said memory with communication parameters newly acquired fromthe particular destination terminal under a normal protocol.
 11. Afacsimile apparatus comprising: a scanner configured to scan data; aprinter configured to print data; and a data communication mechanismcomprising: a communicator configured to perform a pre-communicationprotocol with a destination terminal, and to transmit data to thedestination terminal after the pre-communication protocol; a memoryconfigured to store data corresponding to at least one destinationterminal, and to store communication parameters corresponding to eachdestination terminal, the communication parameters being utilized toperform a communication with the destination terminal; a controllerconfigured, when data corresponding to a destination terminal is storedin said memory, to perform the pre-communication protocol with thedestination terminal, by using the stored communication parameterscorresponding to the destination terminal; and the controller beingfurther configured, when a communication error occurs in a communicationwith a particular destination terminal having data stored in saidmemory, to delete communication parameters corresponding to theparticular destination terminal from said memory.